将XPath翻译成JXPath

Question

我得到了以下XML：

 <?xml version="1.0" encoding="UTF-8"?>
        <CreateReservation>
           <NewReservation>
              <Profile op="D">
                 <ProfileID>ID</ProfileID>
                 <ProfileType>TYPE</ProfileType>
              </Profile>
              <Number>123456</Number>
           </NewReservation>

​

使用JAXB从CreateReservation类封送的方式如下：

CreateReservation request = new CreateReservation("123456", "D");
String xpathExpr = "boolean(//*[local-name()='CreateReservationRQ']//@op='D')"
JAXBContext context = JAXBContext.newInstance(CreateReservation.class);
marshaller = context.createMarshaller();    
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
Document document = db.newDocument();
marshaller.marshal(request, document); //line creates xml presented above

//EVALUATION
XPath xPath = XPathFactory.newInstance().newXPath();
xPath.evaluate(xpathExpr, document, XPathConstants.BOOLEAN); //line evaluates xpath and returns true

总结每一个XML，给出代码封送CreateReservation类，用它创建相应的xml，并使用xpath表达式检查创建的xml是否有任何<CreateReservation>节点，其中有任何带有op="D"属性的子节点。检查使用以下xpath表达式完成：

boolean(//*[local-name()='CreateReservationRQ']//@op='D')

该条件工作良好，为提供的代码示例。现在，我想摆脱不必要的CreateReservation类编组。为此，我想从JAXB切换到JXPath：

PathContext jXPathContext = JXPathContext.newContext(obj);
Object obj = jXPathContext.getValue(CONDITION);
if (obj != null) {
   //code should behave exactly the same, as my previous model
}

obj- CreateReservation类的成员(它的结构与上面的xml完全相同)

CONDITION-我的JXPath查询

这句话的意思是：

  Object obj = jXPathContext.getValue(CONDITION);

当CreateREservation类的op字段等于'D‘时，返回任何节点。如果没有节点出现，则返回null。功能代码的行为应该与以前完全相同。你能告诉我我的CONDITION应该是什么样子吗？

Answer 1

对于动态xpath对象实现，您可以查看以下内容。

示例1: JavaBean属性访问

JXPath可用于访问JavaBean的属性。

 public class Employee {
    public String getFirstName(){
       ...
    }
 }

 Employee emp = new Employee();
 JXPathContext context = JXPathContext.newContext(emp);
 String fName = (String)context.getValue("firstName");

在本例中，我们使用JXPath访问emp的一个属性。在这个简单的例子中，对JXPath的调用相当于在bean上调用getFirstName()。

示例2:嵌套Bean属性访问

JXPath可以遍历对象图：

 public class Employee {
    public Address getHomeAddress(){
       ...
    }
 }
 public class Address {
    public String getStreetNumber(){
       ...
    }
 }

 Employee emp = new Employee();
 ...

 JXPathContext context = JXPathContext.newContext(emp);
 String sNumber = (String)context.getValue("homeAddress/streetNumber");

在本例中，XPath用于访问嵌套bean的属性。xpath标识的属性不必是“叶子”属性。例如，我们可以在上面的示例中提取整个Address对象：

Address addr = (Address)context.getValue("homeAddress");

示例3:设置属性

JXPath可用于修改属性值。

 public class Employee {
    public Address getAddress() {
       ...
    }

    public void setAddress(Address address) {
       ...
    }
 }

 Employee emp = new Employee();
 Address addr = new Address();
 ...

 JXPathContext context = JXPathContext.newContext(emp);
 context.setValue("address", addr);
 context.setValue("address/zipCode", "90190");

示例4:创建对象 JXPath可用于创建新对象。首先，创建AbstractFactory的子类并将其安装在JXPathContext上。然后调用createPathAndSetValue()而不是"setValue“。当JXPathContext发现路径的中间节点为空时，它将调用您的AbstractFactory。它不会覆盖现有节点。

public class AddressFactory extends AbstractFactory {
    public boolean createObject(JXPathContext context,
               Pointer pointer, Object parent, String name, int index){
     if ((parent instanceof Employee) && name.equals("address"){
       ((Employee)parent).setAddress(new Address());
       return true;
     }
     return false;
   }
 }

 JXPathContext context = JXPathContext.newContext(emp);
 context.setFactory(new AddressFactory());
 context.createPathAndSetValue("address/zipCode", "90190");

有关详细帮助，请查看此链接：JxPath教程